The invention relates to a printing table for a flatbed printing machine with a printing table base and a printing table plate disposed on the printing table base, where the printing table base is connected by several connecting elements to the printing table plate.
In large-format printing machines, e.g., for a print format of up to approximately two by three meters, a deviation, even if only very slight, in the planarity of the printing table surface represents a serious problem, in particular in the case of digital flatbed printing machines. This is because, for example, in ink jet printers the ink jet heads must be guided at a constant distance of approximately one millimeter over the medium to be printed on, e.g., a paper sheet, in order to ensure good print quality. Printing table surfaces with only extremely low deviations in their planarity are thus required. With, for example, only local warming of the printing table plate the problem of thermal deformation of the printing table plate arises, which then, for example, causes arching in isolated areas.
With the invention, a printing table for a flatbed printing machine, in particular a digital flatbed printing machine, will be provided which meets the highest requirements with respect to the planarity of the printing table surface.
For this, according to the invention, a printing table for a flatbed printing machine with a printing table base and a printing table plate disposed on the printing table base are provided, where the printing table base is connected by several connecting elements to the printing table plate. The connecting elements permit movement of the printing table plate relative to the printing table base, in particular movement caused by thermal expansion, only in the direction parallel to the printing table surface and only proceeding from a certain area of the printing table plate. The area has the form of a point or line and is fixed relative to the printing table base.
By limiting movement of the printing table plate relative to the printing table base only in the direction parallel to the printing table plate surface, the printing table plate can also expand locally while nonetheless arching is not to be feared. Due to the fact that only expansion proceeding from an area fixed relative to the printing table base is possible, there is on the printing table plate at least one point which is fixed with respect to the printing table base, in which, for example, the origin of a coordinate system of the control of the flatbed printing machine can be set. This fixed point of the printing table plate does not necessarily have to be rigidly connected to the printing table base, or connected to it at all. Rather, the connecting elements can be disposed so that a thermal expansion of the printing table plate is only possible proceeding from an area having the form of a point of line. Through the printing table according to the invention, a high table planarity which is extremely important, in particular in digital printing machines, can be achieved.
In a refinement of the invention, the connecting elements for the application of holding forces in and opposite to a holding direction are provided and with respect to the forces and displacements in the direction perpendicular to the holding direction are formed so as to be essentially bendable or are mounted in such a manner that they can move.
The connecting elements are thus formed essentially as single-valued bearings. Examples of single-valued bearings are rocking supports or roller bearings, in which forces in and opposite to a holding direction can be transmitted, but in the direction perpendicular to the holding direction displacements are possible. Through the use of such connecting elements the danger of distorting stress is clearly reduced since holding forces in different directions are also applied by different connecting elements.
In a refinement of the invention, the connecting elements comprise first connecting elements whose holding direction runs in the direction perpendicular to the printing table surface and second connecting elements whose holding direction runs in the direction parallel to the printing table surface.
According to the invention, a separation of connecting elements for different holding directions is thus provided, whereby the danger of distorting stress and warping is reduced. In addition, a simple, and moreover adjustable, structure results. This is of great importance, in particular for a possible adjustment of the table planarity. The first connecting elements thus hold the printing table at a constant distance from the printing table base and thus are a primary cause for table planarity with extremely small deviations. The first connecting elements can, for example, be adjustable in order to be able to adjust table planarity. As single-valued bearings, the first connecting elements can hold the printing table plate but not against relative movements in the direction parallel to the printing table surface. For this, the second connecting elements are provided, whose holding direction runs in the direction parallel to the printing table surface. The second connecting elements can also apply only holding forces in and opposite to their holding direction so that a second connecting element can also suppress only movement in a single direction lying parallel to the printing table surface. Thus, several second connecting elements are provided whose holding directions do not coincide and are disposed so that a relative movement of the printing table plate and the printing table base in particular sections, in particular due to thermal expansion, is possible only proceeding from a certain area of the printing table plate, the area having the form of a point of line and being fixed relative to the printing table base.
In a refinement of the invention, the second connecting elements are disposed so that each second connecting element is assigned to one of several imaginary lines running in the direction parallel to the printing table surface. The lines run through the printing table plate's point-like area, which is fixed relative to the printing table base, where the holding direction of each second connecting element runs in the direction perpendicular to its respective assigned line.
In this way, an extension of the printing table plate is possible only in the direction along or parallel to the imaginary lines since the second connecting elements can apply holding forces in the direction perpendicular thereto. The second connecting elements can thereby be disposed so that an expansion of the printing table plate is possible only along lines running at different angles through an area of the print pressure plate so that this area is fixed even with thermal expansion of the printing table plate relative to the printing table base.
For example, the imaginary lines can proceed in the form of a ray from one point on the printing table plate. This point can be the center of the printing table plate but also, for example, a corner of the printing table plate. Alternatively to a point-like area, an area in the form of a line can be provided, e.g., a front face of the printing table plate. The holding directions of the second connecting elements would, in this case, then be oriented in a direction perpendicular to the imaginary lines which for their part are oriented in turn in the direction perpendicular to the area in the form of a line.
In a refinement of the invention, the point-like area which is fixed relative to the printing table base is in the center of the printing table plate and second connecting elements are disposed in all four quadrants of the printing table plate and oriented with their holding directions in a direction perpendicular to the imaginary lines which proceed from the center at least at an angle in the set whose elements are 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315°.
Through such a star-like arrangement of the imaginary lines and the corresponding arrangement of the second connecting elements, the center of the printing table plate remains fixed even with thermal expansion of the printing table plate relative to the printing table base, and can at the same time be the origin of the coordinate system of the flatbed printing machine. In other words, due to the special arrangement and formation of the second connecting elements, the printing table plate can only “grow,” corresponding to a thermal expansion, out from its center in the form of a star. However, the center itself is always fixed relative to the printing table base, independently of the type and size of the thermal expansion.
In a refinement of the invention, the first connecting elements are formed as holding bolts, which are disposed in the direction perpendicular to the printing table surface. Advantageously, the holding bolts comprise at least one circumferential groove, and around the area of the circumferential groove, can be bent in the direction perpendicular to their longitudinal extension.
Providing holding bolts permits the realization of a single-valued bearing of the rocking support type, and opens at the same time the possibility of adjusting the printing table plate with respect to its planarity via a longitudinal displacement of the holding bolt. Expediently, several adjustable holding bolts are provided for this purpose, distributed over the surface of the printing table plate. An essentially bendable structure of the holding bolts can be achieved by two circumferential grooves on the holding bolts, where the grooves are at a distance from one another and have a depth, for example, in the range of one half of the radius of the holding bolt. In the area of the circumferential grooves, the holding bolts can thus be bent with little force so that, in case of a thermal expansion of the printing table plate, no significant distortion stress and, caused thereby, warpage of the printing table plate, are to be feared.
In a refinement of the invention, the second connecting elements are formed as holding clips, which are formed for the application of holding forces in the direction parallel to the printing table surface and parallel to their longitudinal extension, and which are formed to be essentially bendable in the direction perpendicular to their longitudinal extension with respect to relative movements of the printing table plate and printing table base.
Providing holding clips makes possible very flat connecting elements which can be disposed without difficulty between the printing table plate and printing table base. The holding clips can, for example, be formed as sheet metal parts, where, by corresponding structuring of the sheet metal blank, holding forces can only be transmitted in and opposite to the longitudinal direction of the holding clips. On the contrary, in the direction perpendicular to the longitudinal direction, the holding clips are deformed by very small forces, so small in fact that, in case of thermal expansion, no distortion stress and, caused thereby, warpage of the printing table plate are to be feared. This also applies for a deformation by turning about the longitudinal direction, the turning also requiring only slight torques. The holding clips formed as sheet metal blanks are structured, for example, in the manner of a leaf spring.
In a refinement of the invention, the holding clips are formed by freely cutting a cover plate of the printing table base and/or a cover plate of the printing table plate.
In this way, a very flat structure can be achieved and the holding clips need no additional space between the printing table base and the printing table plate. The holding clips can, for example, be cut out of the cover plate by such a laser and thus can be produced simply and highly precisely. By realizing the holding clips by means of a free cutting action in a cover plate, no separate components for the construction of the second connecting elements are required.
Further features and advantages of the invention follow from the claims and the following description of a preferred form of the embodiment of the invention in connection with the drawings.